From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
To: Rik van Riel <riel@surriel.com>,
linux-kernel@vger.kernel.org,
Thomas Gleixner <tglx@linutronix.de>
Cc: kernel-team@meta.com, Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Juri Lelli <juri.lelli@redhat.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Steven Rostedt <rostedt@goodmis.org>,
Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
Valentin Schneider <vschneid@redhat.com>,
K Prateek Nayak <kprateek.nayak@amd.com>
Subject: Re: [PATCH v3] sched/mmcid: fix OOB clear_bit when CID is MM_CID_UNSET in fixup path
Date: Tue, 16 Jun 2026 17:40:47 -0400 [thread overview]
Message-ID: <9725f2c5-24fb-4d93-ab8d-33ecaf612ca7@efficios.com> (raw)
In-Reply-To: <20260616203818.1516263-1-riel@surriel.com>
On 2026-06-16 16:38, Rik van Riel wrote:
> In mm_cid_fixup_cpus_to_tasks(), when rq->curr has the target mm and
> mm_cid.active is set, the CID is checked with cid_in_transit() before
> setting the transition bit. In per-CPU mode a newly forked or exec'd
> task can be running with mm_cid.cid == MM_CID_UNSET because CIDs are
> assigned lazily on schedule-in. With cid_in_transit() the guard passes
> for MM_CID_UNSET (no transit bit), converts it to MM_CID_UNSET |
> MM_CID_TRANSIT and stores it back; later mm_cid_schedout() feeds this
> to clear_bit() with MM_CID_UNSET as the bit number, triggering an
> out-of-bounds write.
Thomas, can you have a look as well in case we missed something
subtle ?
Rik, did you check whether there are other instances of that
MM_CID_UNSET issue lurking in the code, or was your analysis
focused on the reproduced bug ?
Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Thanks,
Mathieu
--
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com
next prev parent reply other threads:[~2026-06-16 21:40 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-06-16 20:38 Rik van Riel
2026-06-16 21:40 ` Mathieu Desnoyers [this message]
2026-06-19 19:40 ` Thomas Gleixner
2026-06-19 19:50 ` [tip: core/urgent] sched/mmcid: Fix " tip-bot2 for Rik van Riel
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